Sumanirole (PNU-95666) is a highly selective D2 receptor full agonist with an ED50 of about 46 nM, the first of its kind to be discovered. It was developed for the treatment of Parkinson's disease and restless leg syndrome. While it has never been approved for medical use, it is a highly valuable tool compound for basic research to identify neurobiological mechanisms that are based on a dopamine D2-linked (vs. D1, D3, D4, and D5-linked) mechanism of action.[1][2]